Earth Motion

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Earth Motion

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Early history of astronomy

• Birth of modern astronomy
• 1500s and 1600s
• Five noted scientists
• Nicolaus Copernicus (1473-1543)
• Concluded Earth was a planet
• Constructed a model of the solar system that put
  the Sun at the center, but he used circular
  orbits for the planets
• Ushered out old astronomy

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Early history of astronomy

• Birth of modern astronomy
• Five noted scientists
• Tycho Brahe (1546-1601)
• Precise observer
• Tried to find stellar parallax the apparent
  shift in a star's position due to the revolution
  of Earth
• Did not believe in the Copernican system because
  he was unable to observe stellar parallax

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Early history of astronomy

• Birth of modern astronomy
• Five noted scientists
• Johannes Kepler (1571-1630)
• Ushered in new astronomy
• Planets revolve around the Sun
• Three laws of planetary motion
• Orbits of the planets are elliptical
• Planets revolve around the Sun at varying speed

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Keplers law of equal areas
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Early history of astronomy

• Birth of modern astronomy
• Five noted scientists
• Johannes Kepler (1571-1630)
• Three laws of planetary motion
• There is a proportional relation between a
  planet's orbital period and its distance to the
  Sun (measured in astronomical units (AUs) one
  AU averages about 150 million kilometers, or 93
  million miles)

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Early history of astronomy

• Birth of modern astronomy
• Five noted scientists
• Galileo Galilei (1564-1642)
• Supported Copernican theory
• Used experimental data
• Constructed an astronomical telescope in 1609
• Four large moons of Jupiter
• Planets appeared as disks
• Phases of Venus
• Features on the Moon
• Sunspots

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Early history of astronomy

• Birth of modern astronomy
• Five noted scientists
• Sir Isaac Newton (1643-1727)
• Law of universal gravitation
• Proved that the force of gravity, combined with
  the tendency of a planet to remain in
  straight-line motion, results in the elliptical
  orbits discovered by Kepler

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Constellations

• Configuration of stars named in honor of
  mythological characters or great heroes
• Today 88 constellations are recognized
• Constellations divide the sky into units, like
  state boundaries in the United States
• The brightest stars in a constellation are
  identified in order of their brightness by the
  letters of the Greek alphabet alpha, beta, and
  so on

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Earth motions

• Two primary motions
• Rotation
• Turning, or spinning, of a body on its axis

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Earth motions

• Two primary motions
• Revolution
• The motion of a body, such as a planet or moon,
  along a path around some point in space
• Earth's orbit is elliptical
• Earth is closest to the Sun (perihelion) in
  January
• The plane of the ecliptic is an imaginary plane
  that connects Earth's orbit with the celestial
  sphere

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Motions of the Earth-Moon system

• Lunar motions
• Earth-Moon
• Moon's period of rotation about its axis and its
  revolution around Earth are the same, 27 1/3 days
• Causes the same lunar hemisphere to always face
  Earth

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Motions of the Earth-Moon system

• Eclipses
• Simply shadow effects that were first understood
  by the early Greeks
• Two types of eclipses
• Solar eclipse
• Moon moves in a line directly between Earth and
  the Sun
• Can only occur during the new-Moon phase

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Solar eclipse
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Motions of the Earth-Moon system

• Eclipses
• Two types of eclipses
• Lunar eclipse
• Moon moves within the shadow of Earth
• Only occurs during the full-Moon phase
• For any eclipse to take place, the Moon must be
  in the plane of the ecliptic at the time of new-
  or full-Moon

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Motions of the Earth-Moon system

• Eclipses
• Two types of eclipses
• Lunar eclipse
• Because the Moon's orbit is inclined about 5
  degrees to the plane of the ecliptic, during most
  of the times of new- and full-Moon the Moon is
  above or below the plane, and no eclipse can
  occur
• The usual number of eclipses is four per year

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Lunar eclipse